This core will provide a centralized service for producing the transgenic mice initially required in Program Projects 3 and 7. Specifically, the core will undertake the following procedures: (1) microinjection of fertilized one-cell mouse eggs with specific DNA constructs prepared by Program Project investigators, (2) injection of ES cells in blastocysts, (3) return the eggs or blastocysts to pseudopregnant foster mothers, (4) screen for transgenic offspring by Southern analysis of DNA isolated from tails, (5) organize the mating and pedigree analysis of transgenic mice, and (6) assist in the dissection and analysis of tissues from transgenic mice and embryos. Such a facility is not available at present on the Vanderbilt campus. Therefore, in addition to providing an increasingly important research tool for members of the Program Project, it should also catalyze interaction with other members of the Medical School who may wish to establish the technique, or collaborate on projects related to the expression and mode of action of factors regulating growth and differentiation in vivo.